Update createRasterStack to work with a list of files

[lagerratrobe]

Current behavior uses a Start and End time and tries to stackall files that are available in that timespan. It does this by first checking to see what files exist for this timespan on the remote server and then downloading whatever files are missing. It passes the full list of files to the function and these get processed and stacked.

HOWEVER, if you're working with a subset of hours that span multiple days, this behavior is not what you want, instead, you want to manually download the files you're interested in and the pass in a list of the files that you want stacked.

Add a parameter named "fileList" which is set to NULL by default. When the user passes in a fileList, the function will skip all time based checks and work directly on the list as the source for filenames to stack.

[lagerratrobe]

Updated the function. New function signature looks like this when using fileList param:

  fileList <- goesaodc_listFiles(satID = satID,
                                 datetime = datetime,
                                 endTime = endTime,
                                 timezone = timezone)

  goesaodc_createRasterStack(
    satID = satID,
    datetime = datetime,
    endTime = endTime,
    bbox = bbox,
    dqfLevel = dqfLevel,
    timezone = timezone,
    fileList = fileList)

NOTE: While it seems a bit redundant to have to repeat the satID, datetime etc., I don't think it's bad and am leaving it this way for now.